Composite materials are increasingly used in structural applications due to the high strength-to-weight ratio provided by composite structures. For example, in aircraft construction, composite materials are used in increasing quantities to form the fuselage, wings, vertical fin, horizontal stabilizer, and other components. A wing panel may be produced by co-curing or co-bonding a plurality of elongated composite stringers to a composite wing skin. The process of fabricating each composite stringer may include laying up a stack of uncured composite plies to form a composite charge which may have an approximately flat configuration. Each composite ply may be comprised of reinforcing fibers (e.g., carbon fibers) impregnated with polymer matrix material (e.g., epoxy resin). After layup, the composite charge may be formed over an elongated forming mandrel so that the composite charge assumes an angled configuration corresponding to the cross-sectional shape of the forming mandrel. After forming, the composite charge may be co-cured or co-bonded with other composite parts such as a composite skin.
During forming of the composite charge over an elongated forming mandrel, the opposing ends of the composite charge must be accurately held in position relative to the respective opposing ends of the forming mandrel. In addition, lengthwise tension must be applied to the composite charge during the forming process to reduce or prevent the formation of wrinkles in the composite charge. The lengthwise tension must be continuously applied as the composite charge transitions from an approximately flat configuration to an angled configuration. Furthermore, the composite charge is preferably maintained in centered relation to the forming mandrel during the forming process. After forming, the composite charge must be easily removable from the forming mandrel to allow for high production rates. The above-noted requirements are not understood to be available in known forming systems.
As can be seen, there exists a need in the art for a system and method for accurately holding a composite charge in position relative to a forming mandrel in a manner that allows for the continuous application of lengthwise tension in the composite charge during transition from a flat configuration to an angled configuration, and which preferably provides a means for keeping the composite charge centered over the forming mandrel and which allows for easy removal of the composite charge after forming.